Tips
for selecting and adjusting ergonomic chairs, and sitting properly
Today, in industrialized countries, many people spend the majority of their
waking hours sitting; whether it's at home while watching television or on the
computer, travelling to work in a car or bus, or working at a desk in front of a
computer. Although sitting requires less physical effort than standing or
walking, it puts stress on the lumbar area. The effects of a sedentary lifestyle
combined with a job that requires sitting can lead to many health problems.
Selecting the right chair and adjusting it properly is an important part in
making your workstation safer. Also, learning and practicing how to sit properly
can reduce stress and strain on your muscles, tendons, and skeletal system, and
thereby reduce your risk of developing a musculoskeletal disorder.
Pick a seat
If you work in a sitting position, selecting a suitable
chair is a critical step in preventing health problems. Choose a chair with:
- controls that are easy to operate from a sitting position,
- a seat that adjusts for both height and tilt,
- a seat that does not put pressure the back of thighs or knees,
- a seat with a front edge that curves towards the floor,
- breathable, non-slippery fabric on the seat,
- a backrest shaped to support the lower back,
- a stable five-point base,
- wheels or casters suitable for the type of flooring,
- a swivel mechanism,
- armrests that can be adjusted to the elbow height when your upper arms are
hanging down and your forearms are at about a 90 degree angle to the upper arms,
and
- armrests that do not interfere with free movements within the
workstation.
Adjust your chair to suit
Ergonomic chairs are designed to suit a
range of people; however, a chair only becomes ergonomic when it specifically
suits your body size, workstation, and the tasks that must be performed.
Your chair should be fully adjustable. The optimal seat height is about one
quarter of the body height - a general rule since the torso-to-leg ratio can
vary widely.
- Stand in front of the chair. Adjust the height so the highest point of the
seat, (when in the horizontal position), is just below the knee cap.
- Sit on the chair and keep your feet flat on the floor.
- Check that the clearance between the front edge of the seat and the lower
part of the legs (your calves) fits a clenched fist (about 5 cm or 2 inches).
- Adjust the back rest forwards and backwards as well as up and down so that
it fits the hollow in your lower back.
- Sit upright with your arms hanging loosely by your sides. Bend your elbows
at about a right angle (90 degrees) and adjust the armrest(s) height until they
barely touch the undersides of the elbows.
- Remove the armrests from the chair if this level can't be achieved or if
armrests, in their lowest adjustment, elevate your elbows even slightly.
- Tilt the seat itself forwards or backwards if you prefer.
A well-designed chair allows you to sit in a balanced position. Buying an
ergonomic chair is a good beginning but it may not bring the benefits expected.
The actual sitting position depends on your personal habits; you have to learn
and practice how to sit properly.
Take a good position
A neutral body position is a comfortable
working posture in which your joints are naturally aligned. Working with the
body in a neutral position reduces stress and strain on the muscles, tendons,
and skeletal system and reduces your risk of developing a musculoskeletal
disorder (MSD).
Occupational Safety and Health Administration (OSHA) offers tips on how to
maintain neutral body postures while working at the computer workstation:
- Hands, wrists, and forearms are straight, in-line and roughly parallel to
the floor.
- Head is level or bent slightly forward, forward facing, and balanced -
generally in-line with the torso.
- Shoulders are relaxed and upper arms hang naturally at the side of the body.
- Elbows stay in close to the body and are bent between 90 and 120 degrees.
- Feet are fully supported by the floor or a footrest may be used if the desk
height is not adjustable.
- Back is fully supported with appropriate lumbar support when sitting
vertical or leaning back slightly.
- Thighs and hips are supported by a well-padded seat and generally parallel
to the floor.
- Knees are about the same height as the hips with the feet slightly
forward.
Working in the same posture or sitting still for prolonged periods is not
healthy. Remember to change your working position frequently throughout the day
by making small adjustments to your chair or backrest, stretching your fingers,
hands, arms, and torso, and by standing up and walking around for a few minutes
periodically.
Also, remember that the chair is only one of the components to be considered
in workstation design. All the elements such as the chair, footrest (if needed),
work surface, document holders, task lighting and so on need to have flexibility
and adjustability to be "designed in".
Source:Canadian Centre for Occupational Health and Safety
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